I ain't a girl but I'd suggest you try on some packs with both type of shoulder straps at a backpacking store or two to see what fits you best. Or ask backpacking friends if you can try on their packs.

I currently have a women-specific pack as well as a "unisex" one (which, by default, usually means "men's".) Chris from ULA sent me pictures but the S-straps look a lot curvier than the women-specific packs I've seen/tried on. I don't know if it's just because of the picture -- the packs are flat and not stuffed or being worn.

I was assuming (albeit without much thought) that I would order the S-straps but Chris mentioned that some "more endowed" women have said that they feel "squashed" with them. The ULA website also mentions that the S-straps are favored by thinner people, men included. I guess I'm confused because I thought the whole point of the "S" shape was to accommodate women's "endowments" while fitting narrower shoulders.

They curve away from my neck (1st half of the S), which is probably mostly a benefit for large necked men, but are solving a problem that would not exist if the straps were sown to the pack far enough apart. ie: sown on wider apart for large, than for medium packs.

They curve away from my armpits (2ns half of the S) for easy arm swings with no binding in the armpit. This allows wider straps at the top, without armpit rubbing, but is probably an issue for busty women, especially if they tighten the sternum strap, which pulls the straps further toward the center (even when the sternum strap is worn high, a few inches under the collar bone).

I'd go to REI and look for a pack with extra curvy straps and see how they feel.

I emailed Chris with the same question. I'm a 5'7" 145 lb woman. I have a 2007 Catalyst with J straps (the only type there were then) and they work perfectly for me. I asked Chris about getting S straps on a Circuit. He said he's 5'10", 155 lbs, broad shoulders, thin neck, and he prefers the S straps, but if I got them and didn't like them I could switch them for J's for free shipping. I hadn't thought about my endowments getting squished....hmmm. Any ladies out there tried these Ss yet?